The present invention relates to a device for osteosynthetic fixation of bone fragments, in particular of fragments of a jaw bone. Devices of this type are fitted intraoperatively in order to mutually fix bone fragments which have become separated from each other. This may be necessary either in the context of osteosynthesis, after accidents in which a bone is shattered into bone fragments, or in the context of orthognathic or maxillofacial treatment for surgical control of abnormal positioning after osteotomy and subsequent positional correction of the bone fragments. Such a device principally spans and fixes two bone fragments together, one part of the device in each case being connected releasably to a respective bone fragment. In order to create the connection between tie temporarily fitted device and the bone fragments, the bone plate (which constitutes the essential structural element of the device) has through-holes in which securing elements sit, in most cases bone screws, which engage in the bone fragments. In these devices it is important that the bone fragments are fixed in a stable manner and in the correct position relative to each other.
DE-C-23 40 880 discloses a solid compression plate which is used for treating jaw fractures and which, spanning the fracture site on the jaw bone, is screwed onto both of the bone compartments to be joined together. In each half of the compression plate there are two oblong holes oriented toward the plate center and toward the fracture site. On the side directed away from the jaw bone, the oblong holes have a countersink with a screw seat configured as a beveled plane surface. At least one oblong hole per half is inclined relative to the plate center. On the side directed toward the jaw bone, the bone plate has a projecting notched web at the center. As a result of the arrangement of the oblong holes and the bevelled screw seats, the bone compartments are compressed at the fracture site when the inserted bone screws are tightened. Because of its rigidity, this plate cannot readily be adapted to the existing bone geometry. The simple hole engagement permits little variability in terms of attachment to the bone compartments, and preliminary provisional fixing prior to final positioning is possible only within very limited ranges of movement.
A further refined bone plate for fixation of bone compartments is the subject of WO-A-97 01991. The bone plate described there has at least one continuous screw hole on both its outsides, between which screw holes there is a first axial oblong hole which is limited on both longitudinal flanks by struts lying opposite each other. Moreover, a bracket-shaped retainer is provided for engaging over the bone plate in the transverse direction, i.e. over both struts with the first oblong hole lying between them. The retainer has a second oblong hole which extends transverse to the longitudinal axis of the bone plate and thus also transverse to the first oblong hole. The longitudinal dimension of the second oblong hole corresponds to the width of the first oblong hole. The retainer has two angled guide noses on the outside facing the bone plate, which guide noses engage over and below both struts in the fitted state, so that the retainer is longitudinally displaceable on the bone plate as on a double rail.
In use, one outside of the bone plate is screwed securely to a first bone compartment. The retainer is then temporarily mounted on the bone plate in the area of the first oblong hole and is fixed by means of a locking screw inserted into the second bone compartment after positioning of the movable bone compartment. Said positioning is done by means of longitudinal relative displacement between the bone plate and the retainer within the clearance of the first oblong hole and by transverse relative displacement between the locking screw and bone plate and the retainer within the clearance of the second oblong hole. When bone plate and retainer have been fixed thus far and the bone compartments have been oriented with respect to each other, the remaining outside of the bone plate is screwed to the second bone compartment. Thereafter, the locking screw is unscrewed and the retainer is also removed.
Compared with the earlier state of the art, the bone plate described above resulted in a marked improvement since its flexibility meant that it can be adapted more easily and more accurately to the respective bone geometry. In addition to this, the retainer permits, intraoperatively, an initially approximate and then precise orientation of the two bone compartments which are to be joined together. However, the following shortcomings still remain:
a) The retainer and the associated locking screw are two relatively small and separate individual parts and their application is correspondingly awkward.
b) The length of the bone plate is fixed and is not adaptable to the particular situation. The firs longitudinal oblong hole located in the bone plate is enclosed on all sides and lies between the screw holes, as a result of which there is limited variability in terms of longitudinal mobility.
c) The bone plate can be screwed onto the bone compartments to be joined together only in the area of rigidity; greater variability would also be of advantage here.
In view of the inadequacies of the devices known hitherto for osteosynthetic fixation of bone fragments with a temporarily attached retainer, the object of the invention is to configure the bone plate belonging to the device in such a way as to improve its adaptability to the particular bone situation by easier deformability, simplified choice of length and greater variability in the setting of locally variable rigidities. In addition, it is intended to provide as great as possible a range of clearance or the bone plate provisionally fixed with a retainer. It is also intended to simplify the handling of the hitherto two-part retainer and bone plate during the operation. Finally, it must be possible for the whole device to be manufactured economically in serial production.
In a first embodiment of the fixation device, the bone plate has a longitudinal guide slot which is bordered by plate struts and which is open at one end or closed at both ends. A retainer which can be temporarily attached to the bone plate comprises a disk which engages partially over the bone plate and in which a locking screw sits either in a rotatable manner or fixed, said locking screw being intended to be screwed into a bone compartment via the guide slot. The retainer and bone plate together with the respective bone compartments can be displaced relative to each other within the length and width of the guide slot. A plurality of screw holes are provided on the bone plate, at least at one end. At one end, the bone plate advantageously has an area of members comprising members which can be divided off so as to be able to obtain the desired length in each case. With several possibilities for screwing the bone plate, it is possible to achieve better adaptability to the respective task and improved rigidity across the edge of the bone plate, while the elasticity of the latter can be increased across the surface by means of less material thickness.
The disk fitted on the locking screw of the retainer is advantageously secured against dropping. By this means, an as it were one-piece retainer is obtained whose handling is simplified. A fixing plate is provided for additional stiffening of the screwed-on bone plate and/or for screwing the bone plate at one end, which fixing plate can be mounted on the bone plate screwed on at the other end with bone screws through screw holes.
In a second embodiment, the retainer attached to the bone plate has a plate which engages partially over the bone plate and which can be screwed to the underlying bone compartment laterally to the outside of the bone plate.